Some Aspects of Water Shrew Behavior

The University of Notre Dame

Some Aspects of Water Shrew BehaviorAuthor(s): M. W. SorensonSource: American Midland Naturalist, Vol. 68, No. 2 (Oct., 1962), pp. 445-462Published by: The University of Notre DameStable URL: http://www.jstor.org/stable/2422750 .

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Some Aspects of Water Shrew Behavior M. W. SORENSON

Department of Zoology, University of Utah, Salt Lake City'

ABSTRACT: A 14-month laboratory study was made of some aspects of the behavior of Sorex palustris. An enclosure, simulating the water shrews' natural habitat, was constructed and 13 water shrews, one to seven at a time, were retained for observation.

A 1.5-hour rhythm was evident and consisted of a 30-minute active phase and a 60-minute inactive phase. Laboratory and field data suggested that S. palustris had two major activity peaks which occurred from one hour before sunrise (4:00 AM to 5:00 AM) and from sunset (7:00 PM) to 11:00 PM.

Oxygen consumption rates and food utilization implied that the water shrews required approximately 0.95 g/g/day. It was shown that the animals definitely hoarded food and that a preference existed in the type of food hoarded.

Sensory abilities, tunneling behavior, nesting behavior, inter- and intraspecies behavior were noted. This last behavior was the more pronounced and demonstrated that a dominance hierarchy and territoriality did not exist.

Except for the recent works of Conaway (1952) and Conaway and Pfitzer (1952) only casual observations of the behavior of the water shrew have been reported. The purpose of this paper is to present some additional information about behavioral adaptations displayed by this species.

I wish to express appreciation to J. W. Twente, C. H. Conaway, and T. S. Baskett for their helpful suggestions in the preparation of this paper.

MATERIALS AND METHODS

Thirteen S. palustris, three Peromyscus maniculatus and one Microtus longicaudis were live trapped within a 10-mile radius of Salt Lake City. The animals were retained within a 50-square-foot cage containing a 9-square-foot aquarium. The cage consisted of a 5 x 10- foot frame which supported 3 x 5-foot glass walls. Aluminum strip- ping assured rigidity. Running water, soil, rocks and twigs were ar- ranged to provide a suitable habitat.

Individuals were recognized by trap-inflicted scars or by tail mark- ings made with Vaporite ink every 10 days. Oxygen consumption rates were determined by use of an apparatus described by Farmer and Crampton (1948). Observations were made periodically and randomly. In addition to the surface observations, subsurface activity was noted within tunnels which contacted the glass walls of the enclosure. A portable disc-type recorder was used for rapid note tak- ing during hyperactive periods.

1 Present address: Department of Zoology, University of Missouri, Co- lumbia.

445



446 THE AMERICAN MIDLAND NATURALIST 68(2)

PERIODS OF ACTIVITY

The daily activity cycle of S. palustris within the cage was relatively constant. The environment, with the exception of the tempera- ture which was kept between 15 and 19 C, simtulated the animals' natural habitat.

Natural light was provided for the cage by three small windows. The incident light during daylight periods varied from 0.5- to 2.5- foot candles and averaged 1.5-foot candles. Observations during daylight and during darkness showed that the water shrews' behavior apparently was not affected by light intensity. Night observations were made by ceiling lighting, by focusing a flashlight directly on the water shrews or by using a sniper scope with infrared light.

Definite activity phases alternating with sleeping phases were determined -during 250 observations rmade between 6:00 AM and 12:00 PM. Activities included eating, drinking, nest building, fighting, tunneling and swimming. A major activity peak occurred from sunset (7:00 PM) to 11:00 PM. Field data secured by a trap timing device (Sorenson and Twente, 1961) confirm this activity peak, as well as a secondary peak occurring one hour before sunrise (4:00 AM to 5:00 AM). Between 8:00 AM and 6:00 PM, one or more of the water shrews were above ground and active 55 per cent of the time. In- active phases, with all of the water shrews underground or asleep half the time, occurred at 8:00-9:00 AM, 12: 00-1:00 PM, 3:00-4:00 PM, 5:00-6:00 PM, and 11:00-12:00 PM.

The active and sleeping phases comprised a 1.5-hour rhythm (based on 17 timed observations). The active phase lasted approximately 30 minutes and the sleeping phase, about 57 minutes. The minimum sleeping times were 12 minutes in length and the maximum sleeping times were 130 minutes in length. Activity involving vigorous action was estimated to be less than 15 per cent over a 24-hour period. Mann and Stinson (1957) showed that Blarina brevicauda had an activity rhythm which averaged 2.5 hours. The activity bursts were 49 minutes in length, and the inactive phases were 99 minutes in length. Vigorous activity was determined to be less than 10 per cent over a 24-hour period. Morrison and Pearson (1946) showed that Sorex cinereus had an activity rhythm of 1.4 hours but did not sub- divide this total.

After a sleeping phase, the water shrews normally drank from the aquarium and then wandered along the moss area of the aquarium or near the edge of the cage. Frequently defecation occurred. After one or two minutes, the water shrews went directly to the food plates and ate. Following eating, what may be termed "exploration behavior" took place. The shrews ran into hollow logs and tunnels or scurried along the surface of the cage.

Some of the water shrews were extremely active, moving rapidly from place to place. Others were generally less active, but still displayed hyperactive periods during which they frequently stopped, raised their muzzles and wiggled them for a few seconds. This pat-



1962 SORENSON: WATER SHREW BEHAVIOR 447

tern was consistently interruLpted by scratching periods and two to three additional eating periods.

Following the active phase, the water shrews returned to a nest area and slept. Prior to sleeping, they often walked around in small circles within the nest depression, reminiscent of a dog preparing to go to sleep, and then curled into tight balls. Normally, the tail was placed beneath the body and the muzzle was tucked into the ab- domninal area. This behavior provided a definite starting point for timing sleeping periods as opposed to quiet periods in which the shrews remained motionless on the surface.

Surface activity of the water shrews decreased during the later weeks of captivity. Possibly this decline was caused by increased han- dling, the start of the breeding season, or the fact that cohabiting P. maniculatus were removed. Following a three-week period, two new Peromyscus were introduced into the cage and no immediate increase in the water shrews' surface activity was noted.

The fur around the water shrews' muzzles was often damaged, possibly as a result of ectoparasites. The water shrews vigorously scratched their muzzles with their hind feet and also rapidly bit themselves in what appeared to be an effort to remove ectoparasites. Sev- eral mites (Naemolaelaps glosgowi) including four protonymphs, two adult females and one adult male, as well as nine flea larvae (Si- phonaptera) were removed from one dead water shrew. Ectoparasites were not noted on newly trapped water shrews but apparently were present since the shrews scratched themselves almost immediately upon being released into the cage. Conaway (1952) found the mites, Hirstionyssus and Euphaemogamasus, on newly trapped S. palustris.

FOOD HABITS

The natural diet of S. palustris appears to be mainly aquatic insects. Hamilton (1930) reported that water shrews ate stone fly nymphs, may flies, other aquatic and some terrestrial insects. Dur- ing the present study, seven stomach analyses showed that caddis flies made up about 80 per cent of the natural diet; the remaining 20 per cent was undetermined. Pearson (1947) showed that the digestive cycle of S. cinereus was less than two hours. It is reasonable to suspect that S. palustris also has a very rapid digestive cycle and therefore a precise identification of stomach contents is seldom possible.

The captive water shrews were fed a prepared diet recommended by Pearson (1950) as well as the following modifications which proved acceptable:

(1) beef liver, beef brains and ground beef in equal amounts (2) a 2/3 beef kidney and 1/3 dog food mixture (3) a 3/4 beef liver and 1/4 oatmeal mixture (4) a 1/3 beef liver, 1/3 beef brains and 1/3 cbopped beef suet mixture.

The last diet appeared to be preferred. The prepared diets were given to the water shrews twice daily in frozen chunks of about 50




grams each and they displayed no hesitation in immediately eating the frozen food.

The prepared diet was occasionally supplemented with aquatic insects, terrestrial isopods, earthworms, grasshoppers, fish, oatmeal, lettuce and carrots. The lettuce and carrots were never eaten by the water shrews. Morrison, Pierce, and Ryser (1957) showed that S. cinereus preferred newborn rats and beef liver when given a choice between these and ground beef or worms. At one time two live lizards (Sceloporus graciosus) were placed within the cage. These lizards were located, killed and partially eaten by the water shrews. Heptner (1939) stated that the Turkestan desert shrew (Diplomesodon pul- chellum) also would kill and eat lizards. Springer (1937) stated that under captive conditions, rolled oats were not eaten by Cryptotis parva but that pill bugs were eaten. Svihla (1934) reported that S. palustris ate snails, Microtus and Zapus while in captivity. However, during this study, Peromyscus were not killed or eaten by S. palustris when both species were retained together within the cage. However, on five occasions water shrews did kill and eat each other.

The water shrews varied in their eating places and eating postures. Some remained at the food plates during the entire eating period. Others dragged some of the food off the plates and consumed it within adjacent hollow logs or in the narrow passageway in front of the aquarium about 18 inches away. This latter behavior involved numerous trips with seldom more than a mouthful of food being transported each time. Eating at various food storage areas occurred, but was less frequent than eating at the main food plates.

The water shrews ate rapidly and appeared to tear the food into small chunks by grasping the food with their teeth and then vigorously jerking their heads upward. The forefeet were used to hold the food stationary and to provide leverage during the jerking motion. When they ate oatmeal, the flake was sometimes lifted and held by the forefeet.

Eating periods were consistently short and averaged only V2 to 1 /2 minutes. The average time between eating, based on 51 observations, was 10 minutes, as contrasted with four minutes between eating periods for S. cinereus (Morrison, Pierce, and Ryser, 1957).

The water shrews did, however, go without food for periods in excess of two hours. One shrew, retained in a live trap, did not eat for three hours and 45 minutes. Morrison and Pearson (1946) showed that S. cinereus died after 11 hours without food. Svihla (1934) reported that a captive water shrew (S. palustris) went without food for a two-day period and showed no ill effects. This report prob- ably must be considered an exception.

The water shrews generally drank after eating and sleeping, and always drank following release from a confined area such as a live trap or the metabolism chamber. The shrews drank by lowering theii muzzles to the water level and filling their mouths with water witL




a scooping motion. After each scoop, the muzzles were raised, presumably to facilitate swallowing. On three different occasions, one water shrew did not drink for a six-hour period.

Various foods were stored by the water shrews. Generally, the water shrews ate the different lean meats in the diet and then transported the suet three to seven feet to a cache area. The suet was stored individually by several of the animals in a one-pint Mason jar, until it was completely filled, and then on the surface of the cage adjacent to nest areas. Sometimes the suet was covered with soil or leaves. Surface storage of oatmeal also occurred. One hoard of oatmeal, in and around a nest area, measured about 11 inches in length, two inches in width and three inches in depth.

At three different times over 100 aquatic insects were placed along the moss area of the aquarium. Each time, the water shrews quickly located the insects and immediately ate several of them. Then, individually, they hoarded the remaining insects, one by one, within a hollow log. This process often required 70 or 80 trips and was interrupted by only three or four short periods wherein the shrews drank from the aquarium or ate one of the aquatic insects.

On two occasions when the aquarium was heavily stocked with small fish (green sunfish, suckers, trout, dace, chubs and shiners), certain shrews killed and stored several of the fish. The shrews appeared to have no difficulty in locating the swimming fish and caught the fish by biting them directly behind the head. One of the water shrews successfully caught a small fish in shallow water by jumping onto it from a distance of about five inches. Fish over six inches in length were too heavy for the water shrews to drag over the aquarium edge and were subsequently released. In a four-day period, four water shrews caught and stored in separate piles 19 small fish. No green sunfish were caught, although several only two inches long were present for nine months. Conversely, a large seven-inch green sunfish dragged a swimming shrew under the water.

Fish which remained motionless in the shallow water of the aquarium appeared not to be noticed by the water shrews as no attempts to catch them were observed. Svihla (1934) stated that captive S. palustris did not catch small fish or tadpoles. Conaway (1952) reported that S. palustris did catch small fish in captivity if the fish were active. Both of these observers based their statements on the behavior of an individual water shrew. The observations made on several water shrews during this study support Conaway's statement.

Normally, the stored fish were buried or placed within hollow logs. During a three- to four-week period following storage, most of the fish were dug up and partially eaten by the water shrews. They appeared to accept these decayed fish for food as readily as any other type of food.

METABOLIS M

In order to estimate the daily amount of food S. palustris required, the water shrews' oxygen consumption rates were measured.




During these measurements, the shrews were highly variable in their activity.

The oxygen consumption rates of S. palustris (average weight 11.3 g) varied from a maximum average of 10.9 cc/g/hr to a minimum average of 4.7 cc/g/hr. The average of the means (based on 80 measurements involving five individuals) was 7.8 cc/g/hr, indi- cating that S. palustris required 0.90 Kcal/g/day. These preceding values compare favorably with the oxygen consumption rates of 15.8 cc/g/hr for S. cinereus and 5.3 cc/g/hr for B. brevicauda as determined by Morrison, Ryser, and Dawe (1959).

Literature concerning food consumption by shrews is fragmentary.

TABLE I.-Food consumption or storage in Sorex palustris (avg. wgt. 11.3 g)

Amount eaten Average per or stored individual

Date (grams) (grams) AM PM

8:30-8:30 8:30-8:30 1-4-60 30.2 39.4 13.9 1-5-60 26.3 51.9 15.6 1-6-60 29.1 33.8 12.5 1-7-60 39.3 38.1 15.5 1-8-60 31.6 32.8 12.9 1-9-60 33.1 38.9 14.4 1-10-60 20.5 41.7 15.5 1-11-60 25.2 30.6 13.9 1-12-60 22.8 30.0 13.2 1-13-60 19.1 24.1 14.4 1-14-60 22.5 31.3 18.0 1-15-60 18.4 33.0 17.1 1-16-60 18.3 21.7 13.3 1-17-60 21.7 17.7 13.1 1-18-60 15.5 14.1 14.8 1-19-60 13.8 16.6 15.2 1-20-60 11.6 19.9 15.7 1-21-60 10.3 16.8 13.6 1-22-60 17.2 23.0 13.4 1-23-60 19.5 27.3 15.6 1-24-60 28.1 30.5 14.6 1-25-60 29.1 35.4 16.1 1-26-60 23.5 20.0 14.5 1-27-60 18.8 26.1 14.9 1-28-60 20.0 21.2 13.7 1-29-60 21.8 20.7 14.2 1-30-60 22.3 27.6 16.6 1-31-60 17.7 20.6 12.7 2-1-60 19.3 22.3 13.9

Average 22.4 24.4 14.6




When the total food consumed was measured in grams per day (g/day) and in grams of food consumed per gram of animal weight per day (g/g/day), the two available reports on S. palustris showed: Conaway (1952), four-day observation on one water shrew, 10.3 g/day and 1.0 g/g/day; Svihla (1934), single-day observation on one water shrew, undetermined g/day and 2.5 g/g/day. Blossom (1932) showed that S. cinereus utilized 11.7 g/day and 3.3 g/g/day. Springer (1937) showed C. parva used 5.5 g/day and 1.1 g/g/day. Morrison, Ryser, and Dawe (1959) reported that B. brevicauda utilized 0.56 g/g/day with an average of 1.58 g/g/day. In the course of this study, S. palustris consumed or stored nearly equal amounts of food during day and night periods and averaged 14.6 g/day (Table I). Therefore, S. palustris with an average weight of 11.3 g utilized or stored 1.3 g/g/day. At 1.30 Kcal/g wet weight for the diet, this represented 1.69 Kcal/g/day. When this figure was compared with the expected food consumption of 0.90 Kcal/g/day, derived from the oxygen consumption mean of 7.8 cc/g/hr, it appeared that S. palustris stored approximately 47 per cent of the measured 14.6 grams. Visible food hoards within the cage made this seem reasonable.

At best, the preceding calculations are only indicative, since the diet was heterogeneous and the water shrews showed preferences in the types of food stored. Complete recovery of the food hoards which would have allowed comparative weights was not feasible. However, from the oxygen consumption rate of 0.90 Kcal/g/day (0.68 g/g/day) plus the utilization of hoarded foods, an estimate of 0.95 g/g/day as the food requirement of S. palustris appears reasonable.

NESTING BEHAVIOR

Two one-pint Mason jars, two hollow logs and a system of tunnels made by two Peromyscus and a M. iongicaudis allowed a choice of nest areas for the introduced water shrews. The jars were partially buried to afford concealment along the sides and yet allow observation from the surface. The two hollow logs, one large and containing side cavities and the other one small with only a central hollow core, were placed five feet apart with the hollow areas ob- servable. Quantities of leaves, grass, twigs, horsehair and shredded cloth also were distributed at random within the cage to serve as nesting materials.

The preparation for a nest required considerable time and numerous trips by the individual water shrews to gather the necessary materials. It is estimated that over 100 pieces of cloth were assembled in the formation of one large nest which measured nearly eight inches in diameter. Three other large cloth nests were constructed at different intervals and the largest of these measured about 13 inches in diameter. In contrast, an average of 10 nests measured approximately three inches in diameter.

The process of nest building began with the animal placing it-




self nearly in the center of the gathered material. A series of quick tight turns would then be made to form a small depression. This depression would then be used as a pivot point for the water shrew, which, by using its muzzle in a stitching manner formed the circular walls of the nest. Crowcroft (1955) observed similar stitching behavior by the European water shrew (Neomys fodiens). The muzzle of S. palustris appeared to be of primary importance in nest building while the feet and legs were used only to form the original nest depression.

The water shrews entered and departed from the nests in a burrowing fashion. If the nests were damaged by entering shrews, their muzzles were used to repair the damage. If the nests became too shallow, the shrews would reconstruct the surface of the nests.

New nests were constantly built and old ones constantly vacated or destroyed. On occasion a large nest would be torn down, moved two or three feet, and then reconstructed or subdivided into smaller nests. Often there were more nests than water shrews.

In general, peripheral surface areas of the cage were most frequently used as nest sites. Several nests were made in the hollow logs. Most of these were frequently changed or vacated, but one, constructed in a terminal cavity which afforded two openings, was maintained for a period of about seven months. Small excavations under the hollow logs were made by the shrews and these served as alternate nest areas. Tunnels that could be observed were not used as nest sites. However, it is inferred that there were nests in other tunnels since the water shrews remained underground for periods much longer than their normal activity phases.

TUNNELING BEHAVIOR

The extensive tunnel system, previously noted, was freely used by the water shrews and one long tunnel against a glass wall allowed excellent observation of the water shrews' underground behavior.

The water shrews frequently went into this tunnel for six or seven inches and then backed out. The shrews' movements within the tunnel were sometimes lethargic, although usually rapid. When in motion, the water shrews often flattened their bodies dorso-ventrally by extending their limbs laterally against the sides of the tunnel. This seemed to improve maneuverability and was frequently practiced during encounters with other shrews.

Upon leaving the long tunnel, the water shrews occasionally blocked the entrance with sticks and small chunks of dirt. The dirt pebbles were pushed into the mouth of the tunnel by the shrews' muzzles and forefeet. The sticks, however, were picked up with the teeth and then placed over or into the tunnel entrance. No reason was determined for closing the entrance since the closure was not sufficient to exclude any shrew from the tunnel.

There are few references in the literature relative to tunneling by shrews. Crowcroft (1957) stated that N. fodiens and Sorex araneus




were habitual burrowers. Davis and joeris (1945) stated that C. parva also burrowed. In contrast, Reed (1951) reported that Sorex trow- bridgei never attempted bturrowing in captivity.

During this study, several small tunnels were constructed by the water shrews. These tunnels were made during short bursts of hyper- activity, interrupted by short periods of wandering around the tunnel area. The tunnels were generally started at about a 300 angle from the surface plane and were dug to a depth approximating the shrews' length. These holes were then sometimes abandoned and new tunnels started. Frequently a series of small depressions was dug following antagonistic behavior; this conceivably could be interpreted as displacement behavior. The completion of a tunnel in which the excavation was longer than four or five inches was never observed.

The water shrews primarily used their forefeet for digging. The hind feet threw the detached soil backwards out of the tunnel. On several occasions, burrowing was so vigorous that the loose soil was tossed approximately 15 inches. Crowcroft (1955) stated that the European water shrew used its muzzle extensively while burrowing. In contrast, S. palustris seldom used their muzzles for digging. How- ever, the muzzles were used to reopen a minor tunnel cave-in or to make small depressions in soft terrain. Following this, a shrew would remove the adhering dirt from its muzzle with brisk rubbing by the forefeet.

INTRASPECIES BEHAVIOR

Numerous accounts of antagonism among different species of shrews appear in both popular and scientific literature. Articles in which different species of shrews are depicted as amiable playful creatures also can be found. However, water shrews observed in this study were predominantly antagonistic with more or less stereotyped fighting behavior. Periods without antagonistic behavior appeared to result from mutual avoidance, unawareness, or chance.

On numerous occasions, two water shrews would pass within two inches of each other and no contact would be made. Also, two water shrews would eat without conflict from the same dish separated by only a small ball of food. However, when direct contact between two shrews did occur, rapid squeaking or actual fighting resulted. Obviously, exceptions occurred. When one shrew would touch another shrew's anal region with its muzzle or when two shrews, running rapidly, bumped into each other, aggressive behavior was seldom displayed.

Fighting periods were generally short. Usually one of the water shrews retreated and the other seldom followed. One exceptionally long fight, interrupted by bursts of digging and short eating periods, continued for over one hour and resulted in the death of one of the shrews. Following this fight, the surviving water shrew dragged the dead shrew more than four feet and placed it in the aquarium. The dead shrew was then dragged out of the water and its viscera partially eaten. Rudd (1953) stated that Sorex vagrans, Sorex ornatus and




Sorex sinuosus did not kill each other while in captivity unless food was absent. In this study excess of food was always available. How- ever, five water shrews were killed as a result of fighting.

Fighting was irrespective of sex and was generally preceded by squeaking. The squeaking occurred whenever one water shrew de- tected the presence of another in a restricted area, such as a hollow log, tunnel, nest or narrow passageway. The shrews remained one or two inches apart and one or both emitted a series of rapid, high- pitched squeaks. If neither water shrew retreated, one of the shrews would rise on its hind limbs, exposing its light-colored ventral surface, and again emit a series of squeaks. At this point, the water shrew which remained on all four limbs generally retreated. However, if both animals rose on their hind limbs, and after a series of squeaks neither retreated, actual contact would occur. This pattern of behavior, in which the light-colored ventral surface is exposed, is similar to the aggressive behavior of the European water shrew as noted by Crowcroft (1955). Crowcroft stated that this behavior acted as a bluff during fighting.

Prior to contact one of the S. palustris would slowly move its head to one side then, with its mouth wide open, make a rapid slash- ing movement at the other water shrew's head. If the striking water shrew failed to grasp the other shrew, the. pattern would be repeated. If contact was made, both of the water shrews fell to the ground and curled into an extremely tight ball. In this position, the shrews often rolled several inches over the surface of the cage. When the shrews remained in this ball, serious physical damage often occurred. On several occasions, attempts to separate the animals by inserting a pencil between them were unsuccessful. The fight would end when one of the shrews could no longer continue or when one of the shrews broke the other shrew's grasp and retreated.

Aggressive behavior within tunnels was modified because of the restricted area. As before, preliminary squeaking occurred. Following this phase, if neither water shrew retreated, they would place their backs against opposite sides of the tunnel. This position tended to flatten their bodies and apparently also increased their visible ventral surface. From this semiprone position, one of the water shrews would then attempt to slash at the other shrew's head by lunging forward. If contact was established, the water shrews would again curl into a tight ball and serious injury often resulted. To retreat, one of the shrews would merely turn around and run away.

Following most fights the water shrews utilized either a tunnel, a hollow log or the aquarium for retreat. If possible, retreat was rapid and direct. The defeated shrews seldom engaged in another fight while in the process of retreat; in contrast, the victorious shrews frequently engaged in conflict with other shrews which were accidentally encountered.

The head and the tail were the parts most frequently injured during fights. Tail damage was particularly frequent and many of




the water shrews, after a few weeks in captivity, lost the terminal portion of their tails. This loss appeared to result from an infection following fighting rather than from actual mutilation.

After a fight the distal end of the tail was often curled down and around to form a circle. This posture was retained by the water shrews for relatively long periods. Sometimes this tail posture was so pronounced that the curled tail was placed beneath the shrew's body and forced the animal to walk with its posterior end elevated. Both the victorious and the defeated shrews displayed this tail posture; therefore, it is not a sign of submission.

INDIVIDUAL DOMINANCE AND TERRITORIALITY Aggressive behavior of S. palustris resulted in numerous encounters

and often the victorious shrews were defeated only moments after a victory. On several occasions, water shrews were observed to win and lose several fights during a one-hour period. Only rarely did one individual remain continually victorious over a two- or three-day span. A dominance hierarchy did not exist.

The outcome of these aggressive contacts apparently did not de- pend on the size of the individuals involved or on the territory in which the encounters occurred. The water shrews seldom defended a definite nest area or food cache. One of the most striking facets of behavior of S. palustris was this apparent lack of territoriality.

Newly introduced shrews, as well as resident shrews, often inter- changed nests. Frequently one water shrew would eject another shrew from a nest and then use this nest for a rest period. Displace- ment of the original shrew was accomplished by aggressive behavior in the form of actual conflict or squeaking. The ejected water shrew would then either remain active, or move to an unoccupied nest and continue its sleep period. Sometimes the ejected shrew would forcibly eject another sleeping shrew which would then often continue this behavior pattern. The minimum distance between nests was about 12 to 18 inches, but generally far wider distances prevailed. This spatial arrangement, however, did not appear to be territorial in design since no "private" nests were noted.

Rood (1958) stated that more than one captive B. brevicauda slept in the same nest and that this species was "amiable" and even "playful." Rood interpreted this behavior as a sign of social organization. Conaway (1958) stated that captive C. parva were remarkably social and that community nests were maintained. Crowcroft (1955) reported that the innate aggressiveness expressed by the European water shrew functioned as territorial behavior and that whenever fighting occurred in defense of a nest, the nest owner was consistently dominant. In the present study S. palustris were never noted to occupy a nest at the same time although nest defense did not occur. Therefore, if a social organization did exist among the captive water shrews, it was of a very low order. All of the water shrews ate in- discriminately from food hoards. They also used the same tunnels,




the same food plates and displayed no evidence of individual pathways. Originally, feces were deposited only in the four corners of the

cage, suggesting territorial sign posts. However, with the introduction of new shrews, fecal deposition became random and eventually nearly all of the cage was utilized. The only other behavior exhibited which could be interpreted as territorial behavior, was the marking by defecation on the food plates and the food itself. On several occasions, one water shrew would defecate on a fresh food supply and then leave this food and eat from another food dish. The other water shrews would avoid the marked food and eat from other dishes. This marking was effective for only short periods and often another water shrew would re-mark the same food supply or eat the previously marked food.

INTERSPECIES BEIHAVIOR

The social interaction between several groups of water shrews, numbering from two to seven individuals, and two white-footed deer mice was observed for a 10-month period.

For a short period following release into the cage, individuals of each species were antagonistic towards the other species though actual conflict was rare. Usually one species or the other would be evasive. However, on numerous occasions when Peromyscus and Sorex met and did not avoid one another, as inside a hollow log, the water shrew would emit a series of rapid, high-pitched squeaks and then either the shrew or the deer mouse would retreat. At other times, under similar circumstances, the two animals would quietly remain three to four inches apart and simply wait until one or the other departed.

After several weeks in captivity, the Peromyscus would sometimes attack a water shrew in the open areas. It appeared that the superior agility of the deer mouse was a factor as this aggressiveness only occurred in areas which permitted rapid retreat. On three occasions a trap-killed water shrew was placed in the cage. Each time, the Peromyscus ate the viscera of the shrew and then attempted to carry the uneaten parts underground. The remains were recovered so that the carcass could be further examined. Interpretation of this response is difficult as the Peromyscus in nature avoided traps saturated with shrew odor.

Peromyscus were not noted to disturb the surface nests of the water shrews. Since the deer mice slept underground, it was not determined if the water shrews were aggressive towards the somnolent Peromyscus. Both species used the same tunnel systems and the same food areas.

It seemed that Peromyscus adapted to captivity more successfully than did Sorex. The Peromyscus became fat, remained vigorous and suffered no fatalities. With few exceptions they remained nocturnal and were wary of the observer. In contrast, the weight of the water shrews did not noticeably change. Also, the water shrews did not display an awareness of the observer and were active during the day.




SENSORY ABILITIES

Several workers have commented on sensory abilities of the Soricidae. Blossom (1932) stated that noise had no effect on S. canereus and that near vision was good. Conaway (1952) implied that sight was poorly developed in S. palustris; Svihla (1934) stated that the water shrew used its nose and whiskers underwater to locate snails. Crowcroft (1955) reported that in the European water shrew scent was used for species recognition and also that sex could be determined by the voice in immature water shrews. Lorenz (1952), also working with the European water shrew, reported that they were nearly blind and used their vibrissae to locate food.

Hamilton (1940) stated that captive Sorex fumeus did not hit cage objects, that the sense of smell was not good, that hearing was good and that the tactile vibrissae were acutely sensitive. Rood (1958) reported that the short-tailed shrew (B. brevicauda) displayed acute hearing over several feet, had poor vision, that olfaction was limited to three inches, and that touch and vibration were the best developed senses. Milne and Milne (1948) stated that the average shrew's eyes were only 1/25 of an inch in diameter and therefore undoubtedly inefficient. Southern (1955) implied that shrews relied on a kinesthetic memory.

The cage used in this study contained obstacles, such as rocks, clumps of soil, small piles of twigs, elevated sticks and large hollow logs. The first water shrew released into the cage could not utilize any kinesthetic memory of the terrain or scent pathway system. When this animal was dropped from the live trap near the center of the enclosure it immediately ran rapidly towards the edge of the cage. It veered about three inches from the glass wall and continued running around the periphery of the enclosure. After two complete circuits, the shrew raced several times across the surface of the cage and finally stopped and drank at the moss area of the aquarium. During this period, the water shrew did not run into any of the obstacles but darted around, under, through and between them. This same basic pattern was demonstrated by nearly all of the water shrews introduced subsequently.

During daily activity, the shrews also, displayed an awareness of obstacles, but seldom showed an awareness of being observed. They ran directly to food plates, into tunnels and hollow logs, into one- pint Mason jars and through narrow rock passageways. Only on rare occasions did the water shrews hesitate prior to entering confined areas.

Newly introduced water shrews definitely responded to noise. Hand clapping, key jingling, whistling, recorder clicks, etc., caused the animals to dart for cover. However, after a few hours, only the more pronounced sounds evoked a response and no response was noted to normal conversation. In general, hearing appeared to be acute for a distance of approximately eight feet. Scratching on the cage walls or on the hollow logs in the cage frequently caused the




water shrews to retreat. Vibrations originating from an automatic washing machine sometimes induced the water shrews to run in and out of the hollow logs.

When the water shrews ran along the surface of the cage or were underground in tunnels, a continuous rapid high-pitched squeaking was often evident. This squeaking normally stopped when the water shrews became inactive. No frequency change was noted when the shrews approached objects. However, this phenomenon was not measured electronically. The preceding behavior suggests either the possibility of the utilization of echo-location or that the water shrews' vision is adequate.

The vibrissae of the water shrew do not extend beyond the front of the animal's muzzle, but project laterally from the muzzle. Those at the base of the muzzle are longest. These vibrissae appear to be most useful as lateral feelers within confined areas. When the water shrews gathered aquatic insects from the moss area of the aquarium, the vibrissae appeared to aid in the location of the insects. No use of the vibrissae in finding moving fish was observed; however, observation was difficult because of the speed of the shrew in the water.

The water shrews consistently exhibited what was interpreted to be smelling behavior. They elevated their muzzles and the nasal areas appeared to quiver. This behavior occurred intermittently during all surface activity and could be elicited by putting alcohol-based chemicals near the shrews. Furthermore, when the observer's hand was placed four to six inches from the animals, a positive response was generally shown.

The sense of smell was also indirectly tested in the field. As trapping progressed, it became apparent that the odor of a captured water shrew on the trap itself was a direct stimulus for another water shrew to enter the same trap. For example, in a series of 30 traps covering approximately 450 feet of stream-side habitat, after one water shrew was trapped, the successful trap remained the most productive one in the series. This was further tested by placing 10 live traps within the cage for three days and allowing the water shrews to wander in and out of the traps. Thus they presumably saturated the traps with their odor. These traps were then marked and placed in the field closely adjacent to unmarked traps. All traps contained similar peanut butter and oatmeal bait. Of seven water shrews trapped, six were caught in the marked traps that had been entered by caged shrews. This odor also appeared to repel Peromyscus from entering the traps for a two- to three-day period.

Ground shrew carcasses were added to the bait of another series of experimental traps. These traps were then placed in the field adjacent to traps which contained only a peanut butter and oatmeal bait. Of 16 water shrews trapped, 10 were caught in the traps containing the ground shrew bait.

Attempts to determine experimentally the acuteness of the water shrews' sensory organs were only partially successful. The design of



1962 SORENSON: WATER SiREw BEHAVIOR 459

the cage prevented the isolation of individual shrews and also made the recapture of the water shrews difficult. In addition, the popula- tion remained at a low level. Since only four water shrews were used experimentally, the following restults are inconclusive.

A square 18-inch cardboard barrier with two offset doors, each approximately two inches square, was centered around one of the food plates. After a water shrew entered and started to eat, an electronic strobonar flash unit was positioned two to three inches from the water shrew's eyes and fired. Since the water shrew has rod vision, it was assumed that the intensity of the electronic flash would temporarily blind the animal. After seven of eight flashes, the water shrew ran into the cardboard barrier about nine inches away. The shrew then either climbed over the barrier or ran along the edge close enough for the vibrissae to function until it reached one of the doors. On two other occasions a hyperactive shrew was noted to run into the barrier when the flash was not fired. When the barrier was in position overnight, the water shrews were observed to run through the doors of the barrier without hesitation. When the location of the doors was changed, the shrews continued to run in and out of the doors without delay.

The vibrissae of one of the water shrews were clipped. The animal was then released into the cage and observed for about two weeks. There was no apparent modification in the shrew's behavior. It continued to use the tunnel systems and other confined areas, consistently located its food and did not display any outward change of activity.

The same animal was later recaptured and its eyes were efficiently masked with a viscous hair wax. Prior to releasing the shrew within a square 24-inch single door cardboard enclosure which had been left in the cage overnight, a tunnel under this enclosure was destroyed and additional soil was placed along the sides of the barrier to make further tunneling more difficult. However, upon release, the water shrew ran directly to the site of the destroyed tunnel and burrowed its way out. Following escape, the animal rapidly scurried to an adjacent hollow log and without delay entered one of the small log cavities. Moments later the shrew reappeared and ran a short distance across the surface of the cage. The fact that the water shrew tunneled out at the point where the original tunnel had been closed, and that the shrew located the adjacent log cavity without apparent difficulty, suggests the possibility of a kinesthetic memory.

The eyes and ears of another water shrew were completely covered with viscous hair wax. This shrew was then released into the enclosure described above. The water shrew ran to the side of the enclosure and appeared to bump the wall. At a slower pace the shrew then followed the side of the barrier to a point near the door where it remained motionless for about 30 seconds. The animal then retraced its path and avoiding an obstacle, moved back to the original rielease point. Again it remained motionless for nearly 30 seconds




and then dressed its facial area and returned to the wall near the door. The water shrew then ran through the door and went directly to a hollow log.

In the preceding experiments, contrary to the report by Orr (1949), none of the shrews died from fright. Rather, the water shrews appeared to be quite durable and did not display any apparent deleterious aftereffects.

That S. palustris depends on several senses and also possibly a kinesthetic memory within its environment seems obvious. However, the acuteness of the individual senses needs further investigation.

DISCUSSION During the first 11 months of this study, the water shrews were

not handled. This policy proved to be advantageous since the animals remained above ground and active during long periods, permitting numerous observations to be recorded. During the final six weeks the shrews were used for oxygen determinations and sensory experiments. As these experiments progressed, the water shrews became far less active on the surface and often at the slightest disturbance darted underground where they frequently remained for several hours.

The fact that S. palustris continually hoards large quantities of food in captivity but does not eat these- stores to any great extent, strongly suggests that this behavior is instinctive. That the shrews also show a preference of primarily storing suet which has a high calorific value and does not readily spoil may be also an innate characteristic. Hoarding behavior would permit the animal to have an available food supply during periods when natural food concen- trations were at a minimum and also would reduce the shrew's energy expenditure by allowing the animal to remain in one area for long semiactive periods. Laboratory observations showed that the water shrews would eat from a food hoard, even though this hoard was partially decayed, and that also a shrew went without water for periods longer than six hours. These observations strengthen the possibility that uncaged water shrews may remain in restricted areas over long periods of time.

The data suggest that S. palustris has two major hyperactive periods occurring prior to dawn and shortly after dusk. These times coincide with the demonstrated oxygen consumption peaks in B. brevicauda and S. cinereus (Pearson, 1947). Therefore, it is suggested that S. palustris gathered and stored enough food to meet their re- quirements during these hyperactive periods. Furthermore, these hyperactive periods may reduce over-all energy expenditure by decreasing surface activity and potentially unfavorable climatic extremes.

It has been shown by Morrison, Ryser, and Dawe (1959) that S. cinereus has an average weight of 3.5 g, an average heart rate of 780 beats per minute and a respiration rate of 800 per minute. Assum- ing that the water shrew displays comparable values in relation to its size, any adaptations which would tend to lower these rates, therein




decreasing the animal's energy output and heat loss, would be advantageous. The water shrew's habit of sleeping in a tight ball, reducing its exposed surface area; the animal's use of a tightly woven nest; its use of potentially warmer tunnel areas; and its long rest periods are some adaptations which could conceivably lower its energy losses.

Since water shrews are predaceous in nature, feeding mainly on aquatic insects, it is logical that they should rely on a combination of sensory adaptations. Efforts in the laboratory to determine the acuteness of the shrew's sensory organs were only partially successful; however, certain inferences appear warranted. First, the senses of vision and smell seem to be adequate over short distances. Second, hearing may be the water shrew's most acute sense. Third, the vibrissae of the water shrew do not appear to be of primary importance.

The fact that the water shrews and the Peromyscus lived agreeably together in the cage for over 10 months is not too surprising when one considers that the animals differ in their activity periods and are not dependent on the same food caches or nest areas. This also suggests that S. palustris is not so vicious as has been frequently claimed in both popular and scientific literature.

REFERENCES

BLOSSOM, P. M. 1932. A pair of long-tailed shrews (Sorex cinereus cinereus) in captivity. J. Mammal., 1,3:136-143.

CONAWAY, C. H. 1952. Life history of the water shrew (Sorex palustris navi- gator). Am. Midl. Nat., 48:219-248. AND D. W. PFITZER. 1952. Sorex palustris and Sorex dispar from the

Great Smoky Mountains National Park. J. Mammal., 33:106-108.

. 1958. Maintenance, reproduction and growth of the least shrew in captivity. Ibid., 39:507-512.

CROWCROFT, P. 1955. Notes on the behavior of shrews. Behavior, 8:63-80.

. 1957. The life of the shrew. The Stellar Press, Ltd., Barnet, Herts.

DAVIS, W. B. AND L. JOERIS. 1945. Notes on the life history of the little short- tailed shrew. J. Mammal., 26:136-138.

FARMER, F. E. AND E. W. CRAMPTON. 1948. Apparatus for measuring oxygen consumption of guinea pigs. Can. J. Res., Sec. F., 26:14-17.

HAMILTON, W. J. 1930. The food of the Soricidae. J. Mammal., 11: 27-39.

. 1940. The biology of the smoky shrew (Sorex fumeus fumeus Miller). Zoologica, 25:473-492.

HEPTNER, V. G. 1939. The Turkestan desert shrew, its biology and adaptive peculiarities. J. Mammal., :20:139-149.

LORENZ, K. Z. 1952. King Solomon's Ring. Thomas Y. Crowell Co., New York.

MANN, P. M. AND R. H. STINSON. 1957. Activity of the short-tailed shrew. Can. J. Zool., 3,5:171-177.

MILNE, L. AND M. MILNE. 1948. Insect vision. Sci. Am., 179:42-45.

MORRISON, P. R. AND 0. P. PEARSON. 1946. Metabolism of a very small mam-

mal. Science, 104:287-289.




, M. PIERCE, AND F. A. RYSER. 1957. Food consumption and body weight in the masked and short-tailed shrews. Am. Midl. Nat., 57: 493-500.

F. A. RYSER, AND A. R. DAWE. 1959. Studies on the physiology of the masked shrew Sorex cinereus. Physiol. Zool., 32:256-271.

ORR, R. J. 1949. Death from fright in long-tailed shrews. J. Mammal., 30: 195-196.

PEARSON, 0. P. 1947. The rate of metabolism of some small mammals. Ecology, 28:127-145. . 1950. Keeping shrews in captivity. J. Mammal., 31:351-352.

REED, C. A. 1951. Locomotion and appendicular anatomy in three soricid in- sectivores. Am. Midl. Nat., 45:513-671.

RoOD, J. P. 1958. Habits of the short-tailed shrew in captivity. J. Mammal., 39:499-507.

RUDD, R. L. 1953. Notes on the maintenance and behavior of shrews in captivity. Ibid., 34:118-120.

SORENSON, M. W. AND J. TWENTE. 1961. A timing device suitable for field studies under adverse conditions. Ecology, 42:212.

SOUTHERN, H. N. 1955. Nocturnal animals. Sci Am., 192:89-99. SPRINGER, S. 1937. Observations on Cryptotis floridana in captivity. J. Mam-

mal., 18:237-238. SVIHLA, A. 1934. The mountain water shrew. The Murrelet, 15:44-45.



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Some Aspects of Water Shrew Behavior